There has been so far expected an image sensor which is capable of obtaining a range image of an object. It is also expected that an actual image of an object to be measured and a range image are obtained by the same chip. The above-described range image sensor is expected to be applied to various technologies. For example, where the range image sensor is loaded on a movable body such as a ship, an automobile or aircraft, it is possible to obtain a range image of an object around the movable body. It is, thus, possible to control the behavior of the movable body on the basis of the obtained range image of the object. In factory automation (FA), when a range image of an object is obtained, the range image can be used to inspect and control the object.
A method for measuring a distance includes a TOF (time-of-flight) method. This method requires a light source (such as a pulse laser or a light emitting diode (LED)) and a light receiving element. In a range image sensor which uses a charge distributing structure, a distance is calculated by referring to a ratio of accumulated charges distributed in a certain cycle to accumulated charges different in phase therefrom. In other words, deviation of a phase of reflected return light from a phase of radiated light is taken as a distance up to an object, and charges generated in response to the return light are distributed in synchronization with a modulation cycle of the radiated light. And, a deviation amount of the phase is calculated by using a ratio of the distributed charge quantity.
The above-described method requires accumulation of charges. Therefore, where the method is employed under conditions of strong background light, accumulated capacity is saturated prior to reading a signal, resulting in deterioration of a calculated distance. It is, therefore, necessary to accumulate charges, with influences of the background light (disturbance light) being reduced.
In Patent Literature 1, charges are distributed by two light receiving portions and two accumulated capacities. At an overall imaging region, a plurality of pixels are two-dimensionally arrayed and distance information up to an object which is obtained for each of the pixels is output in a two-dimensional manner. In a structure disclosed in the document, at least two capacitors are provided within one pixel, and these two capacitors are used to cancel charges derived from background light.
A time-domain correlation image sensor disclosed in Patent Literature 2 is provided with one capacitor within one pixel, imparting a distributed signal only via a pair of switches to both electrode terminals of each capacitor to integrate electric current at different times, thereby controlling charges flowing into the capacitor and canceling electric current derived from background light.